Geotechnical and geological characterisation of weathering in the London clay formation of the London Basin

Abstract

This thesis describes work that examined the nature of weathering in samples of the London Clay Formation (LCF) using a range of analytical techniques. Visible-Near-Infrared spectroscopy (VNIRS), X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), and Particle Size Distribution (PSD) tests were carried out on samples taken from 7 boreholes in the upper LCF on Hampstead Heath considered to include weathered material; results were compared to a similar suite of tests from the British Geological Survey ‘Hampstead Heath’ borehole core which was considered to be unweathered. Lithostratigraphic similarity between the shallow cores and the BGS core was confirmed by comparison of PSD data. XRF data indicate that weathering in the LCF was wet and tropical. SEM analyses of selected samples indicate that there are clear mineralogical and fabric indicators of weathering present near-surface in the shallow boreholes but absent from lithologically similar strata occurring at greater depth in the BGS borehole. This indicates that weathering in the London Clay Formation at this site is controlled by lithology. Analyses of the spectral data indicate that a simple visible colour index can be used to identify weathering grade. This robust measure enabled comparison of weathering depth in each core, demonstrating that the depth of weathering corresponds with a change in lithology, either the occurrence of a clay unit or sand unit.

Date of Award	Feb 2018
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Andy Gibson (Supervisor) & Nicholas Paul Koor (Supervisor)